Process of protecting light metals against corrosion



atented May I, 1934 PRDCESS F PROTECTING LIGHT METALS AGAINST CORROSION Pierre Prior,

Paris, France No Drawing. Application April 26,1932, Serial No. 607,670. In France April 2'], 1931 2 Claims.

It is known to protect light metals and alloys either by formation of a layer of oxide by means of an electric current in the midst of a conducting solution, or by deposition of metallic oxides, with 5 or without salt solution.

The present invention has for its objecta process allowing to form a protecting layer, very resistant to corrosion, on aluminiumymagnesium and their alloys.

An extremely satisfactory protection is obtained according to the present process by causing to react, on parts formed of light metals or alloys, an aqueous solution of one or more complex neutral soluble salts, the anion of which compulsorily comprises the fluorine element combined with one or more other elements, the cathion being of any nature, but one of the constituent elements of the salt being placed above aluminium in the se- 20 ries of electro-chemical potentials.

The addition of bodies adapted to dissolve or precipitate the secondary bodies formed by the reaction (such as tartrates, citrates, fluorides, etc.,) can be eiiected without modifying the protection provided by the present process. These additions are not indispensable and 'do not constitute the essential feature of the present invention.

The rapidity and efiiciency of the reaction increase with the temperature and reach their maximum at boiling point.

The duration of treatment of the metal with the bath is substantially of to minutes. It can be prolongated until the end of the reaction.

The following examples are given by way of indication and not in a limiting sense.

Example I 10 grs.

It has been found that the quantity of each of the constituents can vary within wide limits,

but the best results have been obtained by means current, in the midst of an alkali and of a solution composedaccording to the second above example.

It has also been found that the bath can be con= tinuously used by eliminating the totality or a portion of the chemical compounds which are formed during the reaction by simple reagents containing in the anion the fluorine element and capable or not of generating the complex salts such as they are above defined.

By way of indication, the continuous action of the bath of the second above example can be ensured byaddition of titanium fluoride.

Protecting coatings obtained in such baths have a high resistance to the usual oxidation agents and in particular to the saline mist and to the saline solution of perhydrol.

The parts treated according to this process are preferably subsequently coated with another protecting layer which can be composed of greases, oils, waxes, gums, tar, etc.

The present process is not limited to the above mentioned conditions and the quality and aspect of the protecting layer can be varied by modifying the concentration of the bath, or the temperature or duration of treatment, etc.

I claim: 0

1. Process for the formation of coatings for preventing the oxidation on articles made of light metals or alloys such as aluminum, magnesium; which consists in immersing the said articles in a solution comprising about 2 parts of double fluoride of potassium and titanium, 1 part of chromium fluoride and A; part of fluoride of sodium for 1000 parts of water.

.2. Process for the formation of coatings for preventing the oxidation on'articles made of light metals or alloys such as aluminium, magnesium, which consists in immersing the said articles in a solution comprising about 2 parts of double fluoride of potassium and titanium, 1 part of chromium fluoride and part of fluoride of sodium for 1000 parts of water, and in gradually adding fluoride of titanium to the said solution in the course of its use.

PIERRE PRIER. 

